1. Technical Field
Aspects of the present disclosure relate to distributed power systems, particularly a circuit for integrating with or attaching to a photovoltaic panel.
2. Description of Related Art
A conventional photovoltaic distributed power harvesting system multiple photovoltaic panels are interconnected and connected to an inverter. Various environmental and operational conditions impact the power output of the photovoltaic panels. For example, the solar energy incident, ambient temperature and other factors impact the power extracted from each photovoltaic panel. Dependent on the number and type of panels used, the extracted power may vary widely in the voltage and current from panel to panel. Changes in temperature, solar irradiance and shading, either from near objects such as trees or far objects such as clouds, can cause power losses. Owners and even professional installers may find it difficult to verify the correct operation of the system. With time, many more factors, such as aging, dust and dirt collection and panel degradation affect the performance of the solar photovoltaic distributed power system.
Data collected at the inverter may not be sufficient to provide proper monitoring of the operation of the system. Moreover, when the system experiences power loss, it is desirable to ascertain whether it is due to environmental conditions or from malfunctions and/or poor maintenance of the components of the solar power distributed power system. Furthermore, it is desirable to easily locate any particular solar panel that may be responsible for power loss. However, information collection from each panel requires a means of communication to a central data gathering system. It is desirable to control data transmission, to avoid transmission collisions, and ascertain each sender of data. Such a requirement can be most easily accomplished using a duplex transmission method. However, a duplex transmission method requires additional transmission lines and complicates the system. On the other hand, one-way transmission may be prone to collisions and makes it difficult to compare data transmitted from the various sources. Due to the wide variability of power output of such systems, and the wide range of environmental conditions that affect the power output, the output parameters from the overall system may not be sufficient to verify whether the solar array is operating at peak power production. Local disturbances, such as faulty installation, improper maintenance, reliability issues and obstructions might cause local power losses which may be difficult to detect from overall monitoring parameters.
Electric arcing can have detrimental effects on electric power distribution systems and electronic equipment. Arcing may occur in switches, circuit breakers, relay contacts, fuses and poor cable terminations. When a circuit is switched off or a bad connection occurs in a connector, an arc discharge may form across the contacts of the connector. An arc discharge is an electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current flowing through a medium such as air which is normally non-conducting. At the beginning of a disconnection, the separation distance between the two contacts is very small. As a result, the voltage across the air gap between the contacts produces a very large electrical field in terms of volts per millimeter. This large electrical field causes the ignition of an electrical arc between the two sides of the disconnection. If a circuit has enough current and voltage to sustain an arc, the arc can cause damage to equipment such as melting of conductors, destruction of insulation, and fire. The zero crossing of alternating current (AC) power systems may cause an arc not to reignite. A direct current system may be more prone to arcing than AC systems because of the absence of zero crossing in DC power systems.
In Photovoltaic Power Systems and The National Electrical Code, Suggested Practices: Article 690-18 requires that a mechanism be provided to disable portions of the PV array or the entire PV array. Ground-fault detection, interruption, and array disablement devices might, depending on the particular design, accomplish the following actions; sense ground-fault currents exceeding a specified value, interrupt or significantly reduce the fault currents, open the circuit between the array and the load, short the array or sub-array
According to the IEE wiring regulations (BS 7671:2008) a residual current device (RCD) class II device on the direct current (DC) photovoltaic side for disconnection because of ground-fault current is referred to in regulation 712.412.
The use of photovoltaic panel based power generation systems are attractive from an environmental point of view. However, the cost of photovoltaic panels and their relative ease of theft, might limit their adoption for use in power generation systems.
Thus there is a need for and it would be advantageous to have circuitry integrable or integrated with a photovoltaic panel which provides features including: monitoring of the photovoltaic panel, ground-fault detection and elimination, arc detection and elimination, theft prevention and a safety mode of operation while maintaining a minimal number of components in the circuit to decrease cost and increase reliability.